#include <time.h>
#include <limits.h>

int __clock_gettime(clockid_t, struct timespec*);

clock_t clock() {
  struct timespec ts;

  if (__clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts))
    return -1;

  if (ts.tv_sec > LONG_MAX / 1000000 ||
      ts.tv_nsec / 1000 > LONG_MAX - 1000000 * ts.tv_sec)
    return -1;

  return ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
}